The present invention relates to a variable valve control system for an internal combustion engine that is equipped with an intake valve timing control mechanism and an intake valve event and lift control mechanism, and more specifically to a fail-safe technique applicable at the occurrence of a malfunction in the intake valve timing control mechanism. The present invention also relates to a variable valve control method for an internal combustion engine.
There have been proposed various variable valve control systems to vary the intake/exhaust valve lift characteristics of internal combustion engines for improvements in engine output and fuel consumption and exhaust gas purification. Japanese Laid-Open Patent Publication No. H07-139378 discloses a variable valve control system for an internal combustion engine, having an intake (or exhaust) valve timing control mechanism forced to reduce a valve overlap between intake and exhaust valve opening periods upon detection of a failure in an actuation unit of the valve timing control mechanism, so as to maintain a certain level of driving performance. Japanese Laid-Open Patent Publication No. 2000-130196 discloses a variable valve control system for an internal combustion engine, having an intake (or exhaust) valve event and lift control mechanism forced to reduce or cancel a valve overlap between intake and exhaust valve opening periods upon detection of an abnormal condition in the engine. Japanese Laid-Open Patent Publication No. 2003-049671 discloses a variable valve control system for an internal combustion engine, having intake and exhaust valve timing control mechanisms controlled on the basis of fail-safe control data, respectively, upon detection of an abnormal condition in either one of the valve timing control mechanisms. For example, this variable valve control system may be configured to control the normally-functioning valve timing control mechanism according to a fail-safe valve control map while forcibly fixing the abnormally-functioning valve timing control mechanism at the most retarded position. Both of the valve timing control mechanisms can alternatively be fixed at the most retarded positions.